The present invention relates to plasma processing apparatuses and plasma processing methods for processing a film on a substrate-like sample, such as a semiconductor wafer, by using plasma formed inside a processing chamber inside a vacuum vessel in order to manufacture semiconductor devices, such as a semiconductor integrated circuit, and in particular, relates to a plasma processing apparatus and operational method thereof for detecting an end point of the processing that is performed using plasma with respect to a film to be processed.
With miniaturization of semiconductor devices, there is a need for a technique (EPD: End Point Detection) capable of accurately monitoring a fine film thickness of a material to be etched or the amount of generation of a reaction product in an etching process and detecting an end point at an appropriate timing. For example, as one of the methods for detecting an etching end point of a semiconductor wafer, there is conventionally known a method for detecting a change in the intensity of light emission having a specific wavelength corresponding to a target reaction product in plasma during dry etching and then detecting an etching end point of a specific film based on this detection result.
In such a technique, during dry etching of a semiconductor wafer, the intensity of light emission at a specified wavelength in plasma light changes with the progress of etching of a specific film. Therefore, the amount of this change needs to be accurately detected so as to detect the end point of a process, the amount of processing, or the remaining thickness of a film to be processed. In such detection, an erroneous detection and/or a decrease in detection accuracy caused by a fluctuation or variation of a detected waveform due to noise included in the data of the intensity of light emission need to be suppressed.
As the conventional technique for accurately detecting such a change in the intensity of light emission, the techniques disclosed in JP-A-61-53728 and JP-A-63-200533 are known, for example. In JP-A-2000-228397 (corresponding to U.S. Pat. No. 6,596,551), the noise included in the obtained data indicative of a change in the intensity of light emission with respect to a temporal change is reduced using a moving average method, while in JP-A-63-200533, the noise is reduced by performing the first order least mean square approximation.
Moreover, there is also known a technique, in which a reaction product generated in etching is irradiated with light (reference light) from the lateral side of a processing chamber inside a vacuum vessel of a plasma processing apparatus, and the light transmitting through the processing chamber is received with a detector to detect the amount of a reaction product or a distribution of reaction products and also a change in the amount or distribution. In this technique, a reaction product is estimated from the obtained temporal change rate of a reference waveform.
On the other hand, in such a technique, the amount of change of the reference waveform is large when the aperture ratio is large, so a reaction product can be easily detected, but as the aperture ratio decreases, the amount of change of the reference waveform decreases and the change is buried in noise and it is therefore difficult to detect the reaction product. Then, JP-A-2000-228397 discloses a technique, in which noise in a waveform is filtered out with a digital filter to highlight a change and then this change is detected. In this conventional technique, in calculating a temporal change rate of data about light emission, a component with a small change is removed as the baseline. Therefore, only a component with a large amount of change, the component being predicted to correspond to a change of a process to be detected, can be extracted.
On the other hand, as with these conventional techniques, an etching end point determination device, which determines, by emission spectroscopy, whether or not an etching process has reached an end point during etching effected by discharging plasma formed in a processing chamber inside a vacuum vessel, has a problem that every time a wafer is processed, a detection signal is weakened due to the adhesion of deposits or the like and thus the accuracy of detection or determination of an end point decreases. With respect to such a problem, as with the technique described in JP-A-63-254732, for example, there is conventionally known a technique, in which a detection signal is corrected by modifying the gain value and offset value of the detection signal in order to stably detect an etching end point. Moreover, as with the technique described in JP-A-62-165920, there is known a technique, in which correction is made by adjusting a signal, which is captured into a photoelectric conversion unit, to a preset value without adding a gain and offset adjustment functions in order to stably detect an etching end point.